『Abstract
We studied the dissolution of biotite and chlorite in laboratory
systems with flow-through and batch reactors. The initial dissolution
of biotite in the near-neutral pH region, under N2(g)
atmosphere is highly non-stoichiometric. A slow linear release
of iron during a period of weeks indicates a surface-chemical-reaction-controlled
mechanism of release for iron. The release of potassium is much
faster than that of iron. A parabolic dependence of accumulated
release with time suggests a diffusion-controlled mechanism of
potassium release. The rates of magnesium, aluminium and silicon
release are between those for potassium and iron and approach
that of iron with time. There is no significant influence of (bi)carbonate
or pH on biotite dissolution rate or stoichiometry in the pH region
7<pH<8.5. The release rates of elements from chlorite are close
to stoichiometric and similar to the iron release rate from biotite.
In closed batch reactors at near-basic pH the composition of test
solutions in contact with biotite is apparently controlled by
gibbsite (Al), kaolinite (Si) and Fe(III)-(hydr)oxide. We estimated
a turn-over time (101-102 yr) for molecular
oxygen and a time scale (10 months) to develop characteristic
Fe(II) concentrations for a granitic groundwater.』
1. Introduction
2. Experiments
2.1. Mineral characterization and sample preparation
2.2. Experimental procedure
2.2.1. Kinetic experiment
2.2.2. Equilibrium experiments
2.2.2.1. Batch experiments
2.2.2.2. Titration experiments
3. Results and discussion
3.1. Kinetic experiment
3.2. Equilibrium experiments
4. Implications for groundwater redox chemistry
Acknowledgements
References